Logan, > 2) We could split up the fallocate call into multiple calls to zero > the entire disk. This would allow a quicker ctrl-c to occur, however > it's not clear what the best size would be to split it into. Even > zeroing 1GB can take a few seconds, FWIW, we default to 32MB per request in SCSI unless the device explicitly advertises wanting something larger. > (with NVMe, discard only requires a single command to handle the > entire disk In NVMe there's a limit of 64K blocks per range and 256 ranges per request. So 8GB or 64GB per request for discard depending on the block size. So presumably it will take several operations to deallocate an entire drive. > where as write-zeroes requires a minimum of one command per 2MB of > data to zero). 32MB for 512-byte blocks and 256MB for 4096-byte blocks. Which matches how it currently works for SCSI devices. > I was hoping write-zeroes could be made faster in the future, at least > for NVMe. Deallocate had a bit of a head start and vendors are still catching up in the zeroing department. Some drives do support using Deallocate for zeroing and we quirk those in the driver so they should perform OK with your change. -- Martin K. Petersen Oracle Linux Engineering
